Miniaturized electric source

ABSTRACT

A miniaturized electric source having a radioactive source of Beta -radiation and a collector for said radiation, said source and said collector forming the terminals of the electric source, said source comprising a metal disc having coated thereon a tritium compound in solid state and a layer of a solid - state dielectric being disposed between said source and collector.

United States Patent Adler et al.

[ MlNIATURlZED ELECTRIC SOURCE [75] Inventors: Karl Adler, Grenchen;

Georges Ducommun, Feldbrunnen, both of Switzerland [73] Assignee:Biviator S. A. Grenchen,

Switzerland [22] Filed: May 5, 1970 211 App]. No.2 34,734

[30] Foreign Application Priority Data May 7, 1969 Switzerland 7000/69[52] US. Cl. 310/30, 310/3 A [51] Int. Cl. G0ld 7/00 [58] Field ofSearch 310/3 A, 3 D

[56] References Cited UNITED STATES PATENTS 2,837,666 6/1958 Linder310/3 D 2,876,368 3/l959 Thomas 310/3 D 2,774,89l 12/1956 Dziedziula etal. 310/3 D 2,930,909 3/1960 Lieb 3l0/3 D 2,934,887 5/1960 Keller 310/3D Primary Examiner-Benjamin A. Borchelt Assistant ExaminerN. MoskowitzAttorneylmirie & Smiley [57] ABSTRACT 9 Claims, 1 Drawing Figure 'II IPATENTEBUBIZIWH 3,767,947

7 7 A'VIIIIIA I KA R L A DL ER NVENTORG 65 8628 oucormuu 1 MIN IATURIZEDELECTRIC SOURCE This invention relates to a miniaturized electric sourceof the type having a radioactive source emitting B-radiation, acollector for receiving this radiation and output electrodes formed bysaid collector and a terminal connected to said source.

Various sources of this type have been proposed in the past, but nosatisfactory results have been found for a miniaturized source adaptedfor use in a watch as an example, and meeting with all conditions suchas safety, reliability suitablepower output and high life time in theorder of to years.

Tritium (H termed T in the following specification) would be suitable asa radioactive source from a number of points of view, particularly itshalf-life time and the possibility of screening stray radiation, but nosuitable technical solution has been known allowing use of this elementin a miniaturized electric source. Due to its high ability of diffusion,vacuum used as a dielectric between the source and the collector wouldbe destroyed within short time. Accommodation of a sufficient amount ofradioactive material in a miniaturized source used to be a seriousproblem.

This invention aims to overcome the above difficulties and to provide aminiaturized source of high power output and life time, extremely lowvolume and simple construction. This is achieved by providing a sourcecomprising a tritium compound in a solid state, a layer of saidcomposition being deposited on at least one surface of a carrier, andthe space between said source and said collector comprising a layer of asolid state dielectric having a thickness and density proper forallowing passage of said B-radiation at an energy in the order of up to18 keV and for electrically insulating said source from said collector.When using T in a chemically bound solid state the problem of diffusiondoes no longer exist or may in any case be neglected. Even though T andHe produced during operation will diffuse into the space between theradio-active source and the collector during operation, such gases willbe contained in such a small amount between the radioactive source andthe collector that passage of the B-radiation and ionisation are noproblem. As far as ionisation of minute cushions of gases occurs, thisis without effect because the electrical insulation between theradioactive source and the collector is obtained by said layer of solidstate dielectric. For these reasons and since the space betweenradioactive source and collector need not be evacuated, the casing ofthe source must not be tightly sealed. Gases developed in the sourcesuch as He and T do not build up pressure in the casing but will easilydiffuse or flow through small leaks into the ambient atmosphere.Therefore, substantially atmospheric pressure exists in the source thisbeing particularly advantageous because chemically all availablecompounds of T are relatively unstable under low pressure.

This invention will now be explained in detail for one embodiment ofwhich a cross section is illustrated on a substantially enlarged scalein the accompanying drawing.

The source which is of circular shape has a metal disc 1, for instanceof copper, serving as a carrier for the radioacive material. Thismaterial is applied to both surfaces of disc 1 in very thin layers 2.The thickness of such layers 2 is suitably selected in relation to theabsorption of B-radiation of the available energy therein such that theradiation emitted from the innermost portion of such layers still leavesthe layers in an significant amount.

The radioactive material used is a compound of T with an element ofsuitable affinity. MT; is used in the illustrated embodiment, but anyother composition may be used. Similar compounds exist with Zirconium,Yttrium and other elements. The use of the one or other of the availablecompounds is a question of chemical stability and price. ln theillustrated embodiment LiT is applied to carrier 1 in a density of 200mC/cm The coated surface of disc 1 is 2 cm so that the total amount ofLiT is 400 mC in the new state of the source, and it will still be inthe order of 200 mC after about 10 to 15 years.

The radioactive source formed by carrier 1 and layers 2 is enveloped byfoils 3 of plastic material flanged down and over-lapping each otheralong the edge of disc 1. Foils 3 are extremely thin in the order of0.2;]. when their density is lg/cm, this thickness being proper on onehand for allowing passage of the B-radiation from layers 2 through foils3 and on the other hand for electrically insulating the radioactivesource from the collector. The collector is formed by a metallic casing4 for instance of steel comprising two shells frictionally engaging eachother along the rim. Each shell of the casing is coated at its innersurface with a layer 5 of graphite serving as an absorbtion mediumavoiding reflection of electrons from the collector back towards theradioactive source.

The casing 4, layer 5, upper plastic foil 3 and upper layer 2 of LiThave a hole for passage of a terminal wire 6 soldered to plate I. Ametallic screen 7 is fixed on terminal wire 6 for collecting possibleradiation passing through the hole of the collector. Screen 7 and theinner end of terminal 6 are imbedded in a bead 8 of plastic material,this material filling also the space between terminal 6 and thecollector 4, 5, whereby all parts are properly insulated from eachother.

In operation the B-radiation emitted by layers 2 passes through foils 3and is collected by collector 4, 5. In this way the collector is chargedto a high negative potential relatively to disc 1. Due to the extremelythin insulating foils 3 between the radioactive source and the collectorthe electric source hasa relatively high capacity in the order of 1,000pF. This is advantageous particularly when the source is loaded by anoscillator as is usual in electric timepieces,where the currentconsumption is highly variable.

Manufacture of the source is of similare simplicity as its design. Afterapplication of LiT layers 2 and of terminal wire 6 to disc 1, foils areloosely applied and then clamped between'layers 2 and layers 5 of thecollector and simultaneously flanged round the edges of disc 1 byapplying and closing casing shells 4. No evacuation or sealing procedureis required except for application of the insulating bead 8.

The source is extremely compact and flat and is thus highly suitable foruse in watches where it may be accommodated at one side of thetimepiece, or in any other miniaturized electric or electronicinstrument.

What is claimed:

1. A miniaturized electric source utilizing the energy of B-radiationemitted by radioactive tritium, comprisa. a source of B-radiationcomprising a metal disc having coated on at least one surface thereof athin layer of a solid tritium compound;

b. a collector element comprising a metallic casing enclosing said disc;

c. a dielectric layer of plastic foil enveloping said disc, interposedbetween said disc and said collector casing and also enclosed by saidcollector casing, and having a thickness and density adapted to allowpassage of said B-radiation at an energy level in the order of up to 18Rev.

2. A source according to claim 1, wherein said dielectric is a plasticfoil of a thickness in the order of 0.2

3. A source according to claim 1, wherein said source comprises acompound of tritium with one element of the group consisting of lithium,zirconium and yttrium.

4. A source according to claim 1, wherein said compound is applied tosaid metal disc in an amount of 200 mC/cm 5. A source according to claim1, wherein said tritium compound is applied to opposite surfaces of saidmetal disc at a density of about 400 mC/cm 6. A source according toclaim 1, wherein said source is enclosed in two plastic foils flangeddown each over the rim of said metal disc.

7. A source according to claim 1 wherein said collector is a metalcapsule enclosing said source and plastic foil and contacting saidplastic foil.

8. A source according to claim 7 wherein said collector has a hole forpassage of said terminal, the space between said terminal and collectorbeing sealed and insulated by means of a bead of plastic material.

9. A source according to claim 1, wherein the collector surface facingsaid source has a coating of an absorption medium preventing reflectionof electrons back toward the radioactive source.

2. A source according to claim 1, wherein said di-electric is a plasticfoil of a thickness in the order of 0.2 Mu .
 3. A source according toclaim 1, wherein said source comprises a compound of tritium with oneelement of the group consisting of lithium, zirconium and yttrium.
 4. Asource according to claim 1, wherein said compound is applied to saidmetal disc in an amount of 200 mC/cm2.
 5. A source according to claim 1,wherein said tritium compound is applied to opposite surfaces of saidmetal disc at a density of about 400 mC/cm2.
 6. A source according toclaim 1, wherein said source is enclosed in two plastic foils flangeddown each over the rim of said metal disc.
 7. A source according toclaim 1 wherein said collector is a metal capsule enclosing said sourceand plastic foil and contacting said plastic foil.
 8. A source accordingto claim 7 wherein said collector has a hole for passage of saidterminal, the space between said terminal and collector being sealed andinsulated by means of a bead of plastic material.
 9. A source accordingto claim 1, wherein the collector surface facing said source has acoating of an absorption medium preventing reflection of electrons backtoward the radioactive source.